This invention relates to a method of characterizing the occupant of a motor vehicle seat for purposes of allowing or suppressing air bag deployment based on sensed occupant weight and seat belt tension, and more particularly to a method of distinguishing a minimum weight adult from a child on a booster seat.
Vehicle occupant weight detection systems are useful in connection with air bags and other pyrotechnically deployed restraints as a means of characterizing the occupant for purposes of determining whether to allow or suppress deployment of the restraints. For example, it is generally desired to allow deployment for a child or small adult, and to suppress deployment or reduce deployment force for a small child, such as a six-year-old sitting on a booster seat. In the case of infant or child seats (referred to herein collectively as child seats) that are placed on the vehicle seat and cinched down with a seat belt, it is generally believed that deployment should be suppressed entirely.
As disclosed in the U.S. Pat. No. 6,246,936 to Murphy et al., issued on Jun. 12, 2001, and assigned to the assignee of the present invention, a tightly cinched child seat can be distinguished from a small adult (such as a 5th percentile adult female) by detecting the variation in the sensed weight during vehicle movement. The occupant is characterized as a small adult if the variation exceeds a threshold, whereas the occupant is characterized as a child seat if the variation is below the threshold, as a tightly cinched seat belt severely restricts variance.
An issue that is not addressed in the above-mentioned patent, however, concerns distinguishing between a minimum weight adult (such as a 5th percentile adult female) and a child seated on a booster seat. While it is important to reliably distinguish between the small adult and the child on a booster seat, the distinction is often difficult to reliably establish in a weight-based occupant characterization system since both types of occupant can produce approximately the same indicated weight, and the detected pressure variation of the occupants during vehicle movement may be similar. Accordingly, what is needed is a method of reliably distinguishing between a minimum weight adult and a child seated on a booster seat.
The present invention is directed to an improved weight-based occupant characterization method that reliably distinguishes between a minimum weight adult and a child seated on a booster seat. According to the invention, an early characterization of the seat occupant is made in an interval following a transition event such as a door opening or ignition state change that activates the occupant detection system. During this interval, an initial characterization routine monitors the seat belt tension and the raw seat pressure to identify signal values characteristic of a minimum weight adult or a child seated on a booster seat. Essentially, the pressure variation during the initial interval is significantly higher for a small adult than for a child on a booster seat, and the seat belt tension is significantly higher for a child on a booster seat than for a small adult. If the indicated occupant weight during subsequent operation of the vehicle is inconsistent with the initial characterization, the initial characterization is discarded, and the seat occupancy is characterized based on the indicated occupant weight.